Is there a way to wash the walls that'll reveal the earlier paint?

I know that with some paints, if you scrub the wall, they tend to smear off like chalk. In one room, there's a light blue paint and the older paint is darker blue. I think I want to wash the walls down and achieve a 'speckled' effect with the darker blue showing through. Problem is, the paint is years old so it's not something new or recent.Is there a way to wash the walls that'll reveal the earlier paint?
i would try sanding an inconspicuous spot and see if that gives you the desired effect....